It is customary in many industrial water systems, particularly papermaking to add a biocide to the water phase to destroy bacteria which have a detrimental effect on the water quality or the quality of products in contact with these waters, such as the paper products. The biocide is usually pumped or added to the waters as a solution of an active biocide. The biocides usually have a terrible odor and some toxic hazard is involved, such as skin sensitivity, if nothing else. After all, most biocides are lethal in appropriate dosages, to the bacteria contained in these industrial waters. The safety regulations can be costly to administer. The object of the present invention is to solve these handling and exposure problems by inoculating the water system with a biocide insulated by microencapsulation. The capsulating film is then either broken by mechanical energy, such as encountered in pumps and mixers, or hydrolyzed in contact with the industrial waters, thereby releasing the biocide into the contaminated waters.